it'd be that the mechanism allows for multi-key hits per key (unless its restricted to a set of movement keys.. which wouldn't make sense), which would be bannable.
You're right, make sure to block those added presses of Alt, Ctrl, and Shift in keyclone unless your user is actually pressing it, this is proof that Keyclone is "bannable" because it has a "mechanism that allows for multi-key hits per key"